1. Pathways to Biomolecules 3 Lipids, Carbohydrates and Proteins

2. Proteins (biological importance) TypeFunctionExamples StructuralProtection, support, movementSkin, bone, cartilage, ligaments, tendons, muscle, hair, teeth, feathers, beaks, cocoons, insect exoskeletons EnzymesBiological catalystsDigestive enzymes, metabolic enzymes HormonesRegulation of body functionsInsulin, glucagon TransportMovement of compounds between and within cells Haemoglobin, apolipoproteins ProtectiveDefenceAntibodies ToxinsAttackSnake and spider venom Most proteins Energy source (only in extreme circumstances) Muscle loss during starvation Table 12.6, p188

3. Protein structure Primary structure Linear sequence of amino acids, the chemical building blocks of proteins Secondary structure Regular helices and sheets Tertiary structure Folding on top of the secondary structure

4. Primary sequence (amino acid structure) Depends on combination and number of 20 different amino acids Amino acids all have common core structure, but differ in the side chain (Z-group or R-group) amino group carboxyl group side chain pg 188-189

5. Polypeptides (p192) Stringing amino acids together to form proteins (condensation reaction) A polypeptide

6. Secondary structure Alpha helix Beta-pleated sheet Hydrogen bonding occurs between carbonyl oxygen and N-H group of near by amino acid

7. Properties of amino acid side chains

8. Tertiary structure Determined in large part by interactions between side chains Covalent bonding Ionic interactions Hydrogen bonding Hydrophobic interactions

9. Sodium channel (  -helical secondary structure)

10. Anion channel (  -sheet secondary structure) cross-eye stereo view

11. Proteins (enzymes ) as catalysts ( pg 195) Enzymes: Are highly specific (complementary chemistry) Lower activation energy (provides alternative reaction pathway) Bring reactants into proximity Can be regulated (turned “on” or “off”)

12. Pancreatic lipase with lipid substrate in active site cross-eye stereo view Lipid substrate

13. Comparison with inorganic catalysts Enzymes: Produce much faster reaction rates Operate under milder conditions (biologically appropriate temperature, pressure, pH) Are more sensitive (protein will denature under harsh conditions) Are very selective (may be specific for only a single reaction)

14. Denaturation of enzymes Denaturation is the disruption of a protein’s secondary/tertiary structure It is caused by disruption of the chemical interactions that hold the polypeptide chains in place and the formation of new, unfavourable interactions.

15. Denaturation by temperature and pH Optimal temperature is dependent on the organism and where it lives. Enzymes from bacteria that live in hot springs are stable at temperatures well over 60  C.